The invention relates to a method for shaping semiconductor surfaces and an apparatus for carrying out the method.
Optical microcomponents such as e.g. microlenses and microlens arrays have been used for many years in optoelectronics. Convex microlenses can be produced in a particularly simple manner using resoftened photoresist structures (photoresist reflow). The convex forms form automatically during heating as a result of the surface tension in the photoresist and can be transferred by dry etching methods e.g. in silicon semiconductor wafers. The reproducible fabrication of concave structures is significantly more difficult, because a self-aligning photoresist process such as reflow is not available. However, concave microlenses could advantageously be used in numerous applications, such as e.g. for correcting the astigmatism of the output radiation of edge-emitting laser diodes. Usually, an attempt is made to produce concave structures by wet-chemical etching methods utilizing diffusion effects. Owing to poor reproducibility and inadequate surface quality, such methods have not, to date, gained admittance to applications on an industrial scale.
U.S. Pat. No. 5,378,289 describes a method for shaping a semiconductor surface in which a surface made of an amorphous silicon is simultaneously deformed and crystallized by a textured pressure mold which is made of a crystalline silicon and is provided with pyramids being pressed into the amorphous silicon surface under the action of heat. This makes it possible to fabricate a crystalline silicon film that has a textured surface corresponding to the textured surface of the mold used for the pressing process.
It is accordingly an object of the invention to provide a method and an apparatus for shaping semiconductor surfaces which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which specifies a simple and cost-effective method which can be used to achieve the shaping of semiconductor surfaces. In particular, it is an object of the present invention to produce concave surface structures by a method of this type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for shaping semiconductor surfaces. The method includes the steps of providing a semiconductor wafer having a semiconductor surface to be shaped and formed of a compound semiconductor material and clamping the semiconductor wafer in-between two plates. At least one of the plates has a negative form with respect to a desired form to be formed in the semiconductor surface. The semiconductor surface is pressed by the two plates at an elevated temperature and the method is carried out in an atmosphere enriched with an element of the compound semiconductor material.
Accordingly, the present invention relates to a method for shaping semiconductor surfaces, in which a semiconductor wafer with a surface to be shaped is clamped in between the two plates. In which case at least one plate has a negative form with respect to the desired form of the semiconductor surface, and the semiconductor surface is pressed by the plates at an elevated temperature.
Preferably, in this case a first plate has the negative form with respect to the desired form of the semiconductor surface and a second plate has a planar area.
In order to obtain the pressing action, a pressure can be exerted on at least one of the two plates, or on both plates, in a direction perpendicular to the semiconductor wafer. The pressure according to the properties of the semiconductor material to be formed is preferably greater than 1 MPa and the temperature preferably is greater than 600xc2x0 C.
The pressing process can be carried out in an inert-gas or protective-gas atmosphere, for example nitrogen gas or argon gas. If the semiconductor material to be shaped is a compound semiconductor, it is possible, in order to prevent decomposition of the compound semiconductor, to use an atmosphere enriched with an element of the compound semiconductor during the shaping. By way of example, if GaAs is used as the semiconductor to be shaped, the method can be carried out in an atmosphere enriched with arsenic.
In the manner according to the invention, it is possible to fabricate diverse forms such as convex or concave structures in a round or sharp-edged embodiment. In this case, the entire semiconductor wafer can be structured at the same time, thereby ensuring cost-effective mass production.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for fabricating a light-emitting diode. The method includes the steps of providing a semiconductor wafer having a semiconductor surface to be shaped and clamping the semiconductor wafer in-between two plates. At least one of the plates has a negative form with respect to a desired form to be formed in the semiconductor surface. The semiconductor surface is pressed using the two plates at an elevated temperature, resulting in a structure having at least one curved depression produced in the semiconductor surface. An active layer sequence is grown on a section containing the curved depression. The structure is provided with electrical contacts.
In accordance with an added mode of the invention, there is the step of forming the negative form to have convex structures for producing concave structures in the semiconductor surface.
In accordance with an additional mode of the invention, there is the step of growing a Bragg reflector layer sequence before performing the step of growing the active layer sequence on the section containing the curved depression. A further Bragg reflector layer sequence can be grown after the step of growing the active layer sequence on the section containing the curved depression resulting in a vertical resonator laser diode being produced.
With the foregoing and other objects in view there is further provided, in accordance with the invention, an apparatus for shaping semiconductor surfaces. The apparatus includes two plates. At least one of the two plates has a negative form with respect to a desired form to be formed in a semiconductor surface of a semiconductor wafer. A pressing apparatus is provided for exerting a pressure on at least one of the two plates in a direction perpendicular to the semiconductor wafer disposed between the two plates. Dome-shaped structures for distributing a compressive force are disposed on that side of the two plates which is remote from the semiconductor wafer.
In accordance with a further feature of the invention, the two plates include a first plate having the negative form and a second plate with a planar area.
In accordance with an added feature of the invention, the two plates are formed of a material, and at a shaping temperature, the semiconductor wafer to be pressed has a lower hardness than the material of the two plates.
In accordance with a concomitant of the invention, the two plates are formed of silicon, metal, or molybdenum.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and an apparatus for shaping semiconductor surfaces, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.